1. Field of the Invention
The present invention relates to a piezoelectric element, and a liquid jet head and an ultrasonic motor in which the piezoelectric element is used.
2. Description of the Related Art
Researches have been carried out so that a ferroelectric material and a dielectric material are formed into thin films and used as piezoelectric elements in micro electro mechanical systems (MEMS).
Especially, researches are intensively carried out so that an ABO3 perovskite type oxide is formed into a film and put to practical use as the piezoelectric element. Attempts are made to control crystal orientation of the perovskite type oxide and improve characteristics of the element.
For example, in Japanese Patent Application Laid-Open No. H06-350154, an example of the piezoelectric element as a bulk is disclosed. The element has a PZT film of rhombohedral structure or tetragonal structure including lead zirconate titanate (hereinafter referred to as PZT in some case) usually having a composition in a composition range of the tetragonal structure. Moreover, these piezoelectric elements are characterized in that {111} orientation is 70% or more in a direction vertical to the main surface of a substrate in a case where the PZT film is of the rhombohedral structure. Moreover, {001} orientation is similarly 70% or more in a case where the film is of the tetragonal structure.
However, since the material contains Pb as an atom in an A-site, an influence on the environmental is regarded as a problem. To solve the problem, in Japanese Patent Application Laid-Open No. 2005-039166, there is proposed a piezoelectric element in which a BiFeO3 perovskite type oxide is used.
A BiFeO3 compound disclosed in Japanese Patent Application Laid-Open No. 2005-039166 is also disclosed as a material having a large remanent polarization in “Japanese Journal of Applied Physics” 2004, Vol. 43, No. 5A, L647v, and “Science”, 14 Mar. 2003, Vol. 299, No. 5613, p. 1719, and the like. However, it is described that an element other than Fe is used as a dopant, but a piezoelectric material in which a B-site atom is the atom of the element other than Fe is not described.
Moreover, considering that PbTiO3 having the large remanent polarization is not preferably used as the piezoelectric material, it is supposed that the characteristic of a high performance cannot be developed with BiFeO3 only. It is actually disclosed in the invention of Japanese Patent Application Laid-Open No. 2005-039166 described above that atoms of elements such as Mn, Rn, Co, Ni, V, Nb, Ta, W, Ti, Zr and Hf are added as B-site atoms. However, a structure of the tetragonal structure or the rhombohedral structure is only used. Therefore, any displacement characteristic or optical characteristic in a region where a piezoelectric characteristic is improved is no used.